The reaction between sodium and water is a highly exothermic chemical reaction that produces sodium hydroxide (NaOH) and hydrogen gas (H2). When sodium metal is added to water, it reacts vigorously, releasing a large amount of heat and hydrogen gas. The chemical equation for this reaction is:

[ 2Na(s) + 2H_2O(l) rightarrow 2NaOH(aq) + H_2(g) ]

The reaction is so exothermic that it can ignite the hydrogen gas produced, leading to a fire or explosion if not handled properly. The sodium metal reacts with water molecules, breaking them apart and forming sodium hydroxide ions (Na+) and hydroxide ions (OH-). The hydrogen gas is released as a byproduct.

The reason for the vigorous reaction is the high reactivity of sodium, which is a highly electropositive metal. Sodium has a low ionization energy, meaning it readily loses its outermost electron to form a sodium cation (Na+). Water, being a polar molecule, can stabilize the resulting sodium cation by solvating it with its oxygen atoms, which are more electronegative than the hydrogen atoms. This solvation process leads to the formation of sodium hydroxide in the aqueous phase.

The reaction is also exothermic because the formation of new bonds in sodium hydroxide and the breaking of the strong O-H bonds in water release more energy than is required to break the sodium-sodium and hydrogen-hydrogen bonds. According to thermodynamic data, the standard enthalpy change for the reaction is approximately -426.7 kJ/mol, indicating a highly exothermic process.

The reaction is also driven by the formation of hydrogen gas, which is highly flammable. The hydrogen gas produced can ignite in the presence of an ignition source, such as a spark or flame, leading to a fire or explosion. This is why sodium metal is often stored in kerosene or mineral oil to prevent contact with water and to contain any hydrogen gas that might be produced.

In summary, the reaction between sodium and water is a highly exothermic and dangerous reaction due to the high reactivity of sodium and the formation of flammable hydrogen gas. Proper handling and storage of sodium metal are essential to prevent accidents.